Calibration unit for cathode-ray tubes



Jan. 22, 1952 M. E. CHUN CALIBRATION UNIT FOR CATHODE-RAY TUBES 2SHEETS-SHEET l Filed Jan. 5 1951 A TTORNEY.

Jan. 22, 1952 M, E, CHU

CALIBRATIO'N' UNIT FOR CATHODE-RAY TUBES 2 sHFE'rs-srmr a Filed Jan. 5,1951 IVLJULIL JLMLLJJLL INVENTOR. MEI. VIN E. CHU/V Patented dan. 22,1952 CALIBRATION UNIT FOR CATHODE-RAY TUBES Melvin E. Chun, Berkeley,Calif., assigner to the United States of America -as represented by theUnited States Atomic Energy Commission Application January 5, 1951,Serial No. 204,619

4 Claims.

This invention relates to a calibration unit for cathode ray tubes andmore particularly to a circuit for providing an accurately calibratedreference grid trace on the screen of a cathode ray tube. n

In using cathode ray tubes for measurement purposes it is necessary toplace a sheet of transparent material having vertical and horizontalgrid lines inscribed thereon over the screen face of the tube. Such aprocedure then involves calibration of the grid in terms of knownvoltages applied to the deflecting plates of the cathode ray tube.Because of inherent characteristics of the necessary electronic circuitsvariations in the calibration of the tube occur thereby necessitatingfurther calibration.

The present invention provides a circuit for producing an accuratelycalibrated grid on the cathode ray tube screen with the electron beamthereof. With such a device it will be readily apparent that distortionof the calibration lines will be the same as for the measuring trace sothat a high degree of accuracy results.

vIt is therefore an object of the invention to provide a new andimproved method of calibration for a cathode ray tube.

Another object of the present invention is to provide a circuit forinscribing horizontal and vertical grid lines on a cathode ray tubescreen with the electron beam thereof.

l Still another object of the present invention is to provide acalibration unit for cathode ray tubes wherein an accurately calibratedsystem of grid lines is traced on the Viewing screen prior to applyingsignal voltages to the deflecting plates.

ode ray tube utilizing the present invention and portrayingcharacteristics of a device; and

Fig. 4 is an isometric illustration of a stepping relay as utilized inthe present invention.

Referring to the drawing nfdetail, and Fig. 1

inparticular, a pair of terminals 2| and 22 are provided which mayreadily be connected to a source (not shown) of commercial alternatingcurrent, For control purposes there is provided a conventional steppingrelay 26 having an actuating coil 21, a principal contactor 28, and fourbanks 29, 33, 3|, and 32 of twelve secondary contacts. A' full waverectifier 33, having four unidirectional units 31, 38, 39, and 4i)connected in a conventional manner, is utilized to provide energizingcurrent to the coil 21 by connecting the terminal 2| to the junctionbetween the units 3'! and 40, with one end of the coil 21 connected tothe junction between the units 31 and 38 and the other end of the coilconnected to the junction between the units 39- and 40. One side of theprincipal contactor 28 is connected to the junction between the units 38and 39 while the other side thereof is connected to the movable elementof the first bank of contacts which in the normal position, is touchingthe iirst of the twelve contacts. For starting purposes a conventionalnormally open push button 42 is connected between the terminal 22 andthe rst contact ofthe bank 29.'

The relay 25 is constructed so that the principal contactor 28 is closedwhen no current flows through the coil 21. Each time the coil 21 isenergized the contactor 23 is opened and, through a mechanical linkageattached to the plunger 43 disposed through the 'coil 21 and includingla ratchet wheel 44 and pawl 45, the movable element of each bank oftwelve contacts is moved to the next successive' contact. While thedrawing shows the banks 29, 30, 3|, and 32 of contacts in line, theactual disposition of the contacts is about the circumference of acircle with the movable elements of each bank extending radially fromthe rotatable center post coupled to the aforesaid ratchet wheel andpawl. From the foregoing it will be readily apparentv that the movableelements of the banks 29, 30, 3|, and 32 will move successively fromcontact to contact as long as the coil 21 is intermittently energized.

Now consider the operation of the relay 26 with the electricalconnections, as discussed previously, accomplished. It will be seen thatno current will flow in the rectier 36 until the circuit through thepush button 42 is completed to the terminal 22. Thus by closing the pushbutton 42 the coil 21 is energized to open the principal contactor 28and simultaneously to move the movable element of the bank 29 from therst contact to the second. In ordervto provide continuous movement ofthe movable element consecutively to each contact and finally back tothe first contact, each of the second to twelfth contacts of the bank 2Sis connected directly to the terminal 22. Under this last circumstanceit will be readily apparent that a momentary closure of the push button42 will start the sequential operation of the relay 2x5 whereby the coil21 is energized to open the contactor 28 momentarily and to move themovable elements to the next contact of the banks. The opening of thecontactor 28 -tor 49 is connected across the latter and the 'push button42.

A rst source 56 of unidirectional voltage is provided and, asillustrated in Fig'. 1, may com'- prise a series of batteries 51 with apotentiometer 58 connected thereacross. A voltage divider 60 comprisingfive series-connected resistors 6|, 62, 63, 64, and 6 5 of equal valueis connected between the negative side of the batteries 51 and theadjustable arm of the potentiometer E8. rIhe Vnegative side of thebatteries 51 is also connected to the second contact of the bank 30 andthe junctions between the resistors of the voltage divider 60 arerespectively connected to the third, fourth, fifth, and sixth contacts.A further connection of the negative .side of the batteries 51 is madeto a terminal 1| on one side of a four pole double throw switch 12 whilethe movable element of the bank 30 `is connected to two groundedterminals 13 and 14 on the same side of the switch 12. To provide ameans of determining the voltage between the negative side of thebatteries i51 and the adjustable arm of the potentiometer 58 aconnection from each is made to a pair of terminals 16 and 11,respectively, across which may be connected a voltmeter (not shown) Itwill thus be seen that with the movable element of bank 30 at the secondcontact no voltage will appear across the terminals 1| and 13, but that,as the movable element progresses to the sixth contact the voltage atthe switch 12 will increase at each step by an increment amounting to 20per cent of the voltage appearing across the tei'- minals 16 and 11.

A second source 8| of unidirectional voltage is provided and maycomprise a series of batteries 8 2 with a potentiometer 83 connectedthereacross. A voltage divider S6 comprising five series connectedresistors 81, 88, 89. 90, and 9| of equal value is connected between thenegative side of the batteries 82 and the adjustable arm of thepotentiometer S3. The negative side of the batteries 82 is alsoconnected to the seventh contact of the bank 30 and the junctionsbetween the resistors of the voltage divider 86 are respectivelyconnected to the eighth, ninth, tenth, and eleventh contacts. A furtherlconnection of the negative side of the batteries 82 is made to theremaining terminal 30 of the switch 12 on the saine sideas theabove-mentioned connections thereto. To provide means of determining thevoltage between the negative side'of the batteries 82 and the adjustablearm of the potentiometer 83 a connection from each is made to a pair ofterminals 98 and 99, respectively, across which may be connected avoltmeter (not shown) From the foregoing it is seen that as the movableelement of the bank 30 moves from the sixth to the seventh contact novoltage appears across the terminals 96 and 14 of the switch 12, butthat, as the movable element moves successively from the seventh to theeleventh contact a' voltage appears across such terminals whichincreases in increments amounting to twenty per cent of the volt-l ageacross the terminals 98 and 99.

Connected between the terminals 2| and 22 is a device |0| for supplyingan adjustable alternating current. The primary winding of a transformer|02 is connected between the adjustable element of the Vdevice |0| andone side thereof.

A half wave rectifier |03 and a series connected resistor |04 isconnected across the secondary winding of the transformer |02 whereby apulsating direct current is developed across the resistor |04. One sideof the resistor |04 is connected to each of the seventh to eleventhcontact of the bank 3| while the other side of the resistor |04 isconnected to the rst contact which is, in turn, connected to the movableelement of the bank 30.

i The movable element of the bank 3| is connected vto the terminal 1| ofthe switch 12. Thus it will be apparent that the voltage across theresistor |013 will appear between the terminals 1| and 13 of the switch12 each time the movable element of the bank 3| is located at one of theseventh to eleventh contact of the bank 3 I.

A device |03 for supplying an adjustable alternating current isconnected between the terminals 2| and 22. The primary winding of atransformer |01 is connected between the adjustable sating directcurrent is developed across the resistor |09. One side of the resistor|09 is connected'to Veach of the second to sixth contact of the bank 32while the other side of theresistor is connected to the first contactwhich is,

y in turn, connected to the first contact of the bank 3|. The movableelement of the bank 322 is connected to the terminal 9B of the switch12. Thus vit will be apparent that the voltage across the resistor |09will appear between the terminals 14 and Srof the switch 12 each timethe movable element of the bank 32 is located at one of the second tosixth contact of the bank 32.

A central terminal which is in line with the terminal 1| of the switch12, is connected to one of the horizontal deecting plates of aconventional cathode ray tube l5. A second central terminal H6, which isin line with the terminal 13 of the switch 12, is connecter-l` to thesecond horizontal deiiecting plate of the tube H5. A third centralterminal ||1, which is in line with the terminal 14 of the switch 12, isconnected to one .of the vertical deecting plates of the tube H5. Tocomplete the connections between the switch 12 and the tube ||5 aconnection is made from thereinaining central terminal ||8 of the formerto the other vertical deflecting plate of the 1atter. 4

To supply suitable operating potentials to the cathode ray 'tube H5,there is provideda conventional power'supply |2|. Ihe various elementsof the tube ||5 are connected to terminals of the power supply |2| whichbear the proper potential relationship with respect to one another.

From the foregoing it will be apparent that sequentially impressedvoltages at such terminals f are applied to the deflecting plates of thetube.

Consider now the operation of the above-described circuit with theterminals 2| and 22 suitably energized by a source of alternatingcurrent and the power supply |2| turned on. Under such circumstances theclosing of the push button 42 starts the sequence of operation bycompleting the circuit through the full wave rectifier 36 to energizethe coil 27 of the relay 25. As has been described previously themovable elements of the banks 29 to 32 of contacts travel simultaneouslyand successively from contact I to I2 and back to contact I. During thetime the movable elements rest on contact I of the banks 29 to 32 thereis no voltage appearing across any of the terminals of the switch 72.When the movable elements touch contact 2 of the banks 29 to 32 it willbe seen that no voltage is impressed across the terminals 7| -and 73 ofthe switch 'I2 but that a voltage equal to that across the resistor |29is impressed across the terminals 74 and 95 of the switch 72. With themovable elements of the banks 29 to 32 at contact 3 of each bank, avoltage equal to that across the resistor 6| appears across theterminals 7l' and 73 and a voltage equal to that across the resistor|5229 again appears across terminals 74 and Q55-, Thus, each time themovable elements travelto successive contacts of the banks 2S to 32 thevoltage appearing across the terminals 7i and 73 increases by a twentyper cent increment of the total voltage across the terminals 76 and 7land an equal voltage appears across the terminals 75 and 96 at eachcontact. The foregoing occurs until the movable elements reach contact 7of the banks 29 to 32, at which time the voltage across the terminals 74and 96 of the switch 72 is zero while the voltage across the terminals7| and 'I3 is equal to the voltage of the resistor E013. As the movableelements move across the remaining contacts of the banks 29 to 32 avoltage equal to the resistor |64 appears across the terminals 7| and 73at each contact and a voltage which increases from zero, in twenty percent increments, to the value of the voltage across the terminals 98 and99 appears across the terminals le and f 9S. The foregoing voltages havebeen illustrated in Figs.` 2A and 2B which illustrate the timecorrelation between the voltages across terminals 7| and 73 and thoseacross terminals 74 and 96, re-

spectively, during one cycle of operation of the relay 25.

Now, with the switch '|2` thrown into position to connect the terminals7|, 73, 74, and 9B to the deflecting plates of the cathode ray tube H5,it will be seen that the voltages applied to the horizontal deflectingplates corresponding to the second to sixth contacts provide successivehorizontal deflections of the cathode ray tube electron beam. At thesame time voltages are impressed on the vertical deflecting plates ofthe tube I l5 which deflect the beam in a vertical direction. The resultof these voltages is to trace ve vertical lines with the electron beamon the screen of the tube I|5, as illustrated in Fig. 2C. A similarcombination of deiecting voltages, as shown in Figs. 2A and 2B, duringthe time the movable element of the relay 26 traverses the seventh toeleventh contacts of the banks 29 to 32 results in ve horizontal tracelines on Athe screen of the tube I I5, as shown in Fig. 2D. The

resultant trace on the screen of the tuber||5 is an accurately denedsystem of grid lines, as shown in Fig. 2E.

After a system of grid lines has been traced on the screen of thecathode ray tube I I 5, as explained above, the switch 72 may be throwninto the opposite position to connect a device |25, the characteristicsof which it is desired to measure, to the deflecting plates of the tube.Such a device |25 may be any electrical apparatus, for example, amagnetic winding of which it is desired to determined thecurrent-voltage characteristic. In the latter instance a voltageproportional tothe current through the device |25 may be connected totwo of the terminals of the switch 72 leading to the horizontaldeflecting plates of the tube ||5 while the voltage of the device |25 isconnected to the other two terminals of the switch 72 leading to thevertical deiiecting plates. Withsuch connections made when the switch 72is thrown in the last mentioned position, a trace is formed across thescreen of the tube H5, as shown in Fig. 3, vshowing the relation betweenthe current and voltage which may be readily and accurately measured byusing the calibrated system of grid lines.

The foregoing system may readily be used where the cathode ray tube hasla persistent screen. However, if such a cathode ray tube is notavailable, a camera or other photographic means may be positionedadjacent the cathode ray tube screen to record the system of grid linesand then later the `characteristic desired to be measured.

With the above-outlined apparatus and procedure it will be readilyapparent that the time characteristic may be measured as well as thecurrent-voltage characteristic. That is, it is possible to introducetime into the measurements by grid modulation of the cathode ray tube H5and this may be done with a conventionalv circuit interrupter insertedbetween the power supply I 2| and the grid of the tube H5. It will alsobe apparent that a grid system having more than the five vertical andfive horizontal lines, as described in the foregoing, may easily beVobtained by utilizing a relay having a sumcient numberof contactsconnected in the manner shown.

While the salient features of the present invention have beendescribed'in detail with respect to one embodiment it will. of course,be apparent that numerous modifications may be made within the spiritand scope of this invention and it is therefore not desired to limit theinvention to the exact details except insofar as they may be defined inthe following claims.

What is claimed is:

1. In a calbrating deyice for a cathode ray tube having an electron gun,a pair of horizontal de- Ilecting plates, a pair of vertical deectingplates, and a viewing screen, the combination comprising means connectedto said electron gun for projecting an electron stream therefrom, meansconnected to said horizontal deflecting plates for impressing a seriesof successively increasing pulses of voltage, means connected to saidvertical plates for impressing a series of equal pulses of voltagehaving a repetition rate equal to that of said series of increasingpulses of voltage, and means connected to the aforementioned means forinterchanging said latter two connections.

2. In a calibrating device for a cathode ray tube having an electrongun, a pair of horizontal deecting plates, a pair of vertical defiectingplates, and a viewing screen, the combination comprising means connectedto said electron gun for projecting an electron stream therefrom, afirst and'- second source of unidirectional voltage each having aplurality of taps for supplying increasing incremental portions of saidvoltage, a third: and fourth source' of unidirectional voltage eachhaving' a constant value, automatic relay means interconnected betweensaid sources and said deecting plates for applying said incrementalvoltages of said rst source to said horizontal plates and said constantvoltage of said third source to said vertical plates in synchronsm withsaid incremental voltages, and then applying said incremental voltagesof said second source to said vertical plates and said constant voltageof said' fourth source to said horizontal plates in synchronism withsaid incremental voltages.

3. In a calibrating rdevice for a cathode ray tube having an electrongun, a pair of horizontal dee'cting plates, a pair of verticaldeiiecting plates, and a viewing screen, the combination comprisingmeans connected to said electron gun for project-ing an electron streamtherefrom, a Erst source of unidirectional voltage including a voltagedivider having a plurality of voltage points, means connected betweenthe voltage divider of Said first source and said horizontal plates forsuccessively applying the voltage of each voltage point thereto, asecond source of unidirectional voltage, means connected between saidsecond source and said vertical plates for applying a constant voltagethereto each time voltage from said rst sourcefis applied to saidhorizontal plates, a third source of unidirectional Voltage including avoltage dividerr having a plurality of voltage points', means connectedbetween the voltage divider of s'aid third source and said verticalplates for successively applying the voltage of each voltage pointthereto, a fourth source of unidirectional voltage, mean connectedbetween said fourth source and said horizontal plates for applying aconstantvoltage thereto each time that voltage from said third sourceis' applied to said vertical plates.

4. In a Calibrating device for a cathode ray tube having an electrongun, a pair of horizontal deecting plates, a pair of vertical deectingplates, and a persistent viewing screen, means connected to saidelectron gun for projecting an electron stream therefrom, a plurality ofcontacts arranged in at least three banks,` each o1' said banks ofcontacts disposed in a circular arf ray about a central rotatable shafthavinga projecting contacting elementfor each bank, a iirst voltagedivider having a plurality of taps connected to a similar number ofconsecutive contacts of the rst bank, a second voltage di'- vider havinga plurality of taps connected to a similar number of contacts rof saidiirst bank, means connected across each of said voltage dividers forimpressing a predetermined unidirectional voltage, one side of saidfirst voltage di-r vider being connected to one of said horizontaldeflecting plates and the contacting element of said first bank beingconnected to a common con-A nection between the other horizontaldeiiecting plate and one of said vertical deflecting plates, one side ofsaid second voltage divider being con# nected to the other verticaldeiiecting plate, a' first source of unidirectional voltage having oneside connected to a plurality of contacts of the second bankcorresponding to the contacts of said rst bank whichy are connected tosaid second voltage divider, the other side of said first source beingconnected to said contacting element of said first bank and thecontacting element of said second bank being connected to said one ofsaid horizontal deflecting plates, a second source of unidirectionalvoltage having one side connected to a plurality of contacts of thethird bank corresponding to the contacts of said first bank which areconnected to said first voltage divider, the other side of said secondsource being connected to said contacting element of said rst bank andthe contacting element of 'said third bank being connected to said othervertical defflecting plate, and means connected to said rotatable shaftfor rotation thereof.

MELVIN E. CHUN.

REFERENCES CITED 'Ihe following references are of record in the iile ofthis patent:

UNITED STATES PATENTS Number Name Date 2,171,216 Koch i-; Aug. 29, 19392,443,794 MacNichol, Jr June 22, 1948 2,448,762 Beste Sept. 7, 19482,449,093 Weingarten Sept. 14, 1948 2,465,355 Cook Mar. 29, 1949

